DESCRIPTION: (Verbatim from the Applicant's Abstract) This project evaluates the extent to which recovery from stroke depends on restitution of function in temporarily impaired cerebral tissue versus reorganization in unaffected brain. A new, dynamic 133 Xenon clearance single Photon Emission Computed Tomography (SPECT) technique, that provides quantification of absolute rCBF through the entire brain, will be used to separate permanent from temporary brain dysfunction following stroke as well as help identify the extent to which unaffected brain can compensate for permanently damaged function through the rCBF patterns elicited by motor and cognitive tasks. High filed (4.1 Tesla) functional magnetic resonance imaging (fMRI) during additional sensory motor and cognitive tasks will be used to compliment and further refine the regional activation data identified in individual patietns by Xenon SPECT. Xenon SPECT during rest and CO2 stress will initially serve to identify diaschisis in peri-infarct regions by determining the volume of brain tissue with reduced blood flow which is in excess of the measured anatomic infarction size. Xe SPECT and fMRI scans during cognitive task activation will ten be used to examine the functional status of peri-infact regions and address the possibility of reorganization in spared brain. A series of tasks that normally induce hemisphere and region specific rCBF activation will provide evidence for cross-hemispheric of ipsilateral compensation during recovery and will also be used to help assess the status and viability of low flow tissue. 128 unilateral stoke patietns and 40 controls will be followed with all neuroimaging procedures at 1 month, 6 month, and 1 year intervals. Neurological, behavioral and cognitive status evaluations will be conducted at the same intervals, providing correlatable functional status data. The extent to which recovery of function may involve "relearning" by brain regions not affected by the stroke will be assessed by evaluating, in well recovered patients, rCBF patterns during cognitive tasks that were initially compromised. Evaluation will consist of comparison with normal controls performing identical tasks. The overall study will provide rationale, based on physiological measurements, for patient management and rehabilitation strategy, including the use of facilitatory versus compensatory rehabilitation techniques.